1. Field of the Invention
The present invention relates to an impact energy absorbing structure for a vehicle and, more particularly, to an impact energy absorbing structure capable of absorbing impact energy to reduce shocks that act on a passenger in the case of a lateral collision of the vehicle with an obstacle, and having shock absorbing means incorporated into an inner panel of a side door of a body of an automotive vehicle, capable of preventing the production of flaws, such as permanent dents, by light pressure applied thereto by the passenger and capable of exerting sufficient impact energy absorbing ability in the case of a lateral collision.
2. Description of the Prior Art
Japanese Utility Model Laid-open (Kokai) No. 61-171620 discloses a side door having an inner panel provided with shock absorbing pads to protect the passenger from injury in case of a lateral collision of the vehicle with another vehicle. The shock absorbing pads absorb lateral impact energy applied to the body of the vehicle so that the passenger will be subjected to reduce impact energy. The shock absorbing pads include a chest protecting pad and a lumbar protecting pad that are substantially the same in rigidity and in thickness, i.e. the size with respect to the width of the body of the vehicle. FIG. 1 shows a basic construction of conventional impact energy absorbing structure, which is constructed by attaching a shock absorbing pad 3, such as a urethane foam pad, to a door inner panel 2 attached to a side door 1.
The basic construction shown in FIG. 1 is practiced in the form of the following specific structures. In an impact energy absorbing structure shown in FIG. 2, the shock absorbing pad 3 is coated with a sponge sheet 4, and the sponge sheet 4 is coated with a hard skin 5. In an impact energy absorbing structure shown in FIG. 3, the shock absorbing pad 3 is covered entirely with a cover 6 formed of a material having a high degree of rigidity, such as a hard plastic plate.
The impact energy absorbing structure of the basic construction shown in FIG. 1 has a disadvantage that a permanent dent 8 or the like is liable to be formed in the shock absorbing pad 3 by pressure applied thereto by the finger or body of the passenger or by luggage. In the impact energy absorbing structure shown in FIG. 2, the same pressure forms a somewhat smaller dent in the shock absorbing pad 3 and the dent may be concealed under the sponge sheet 4, however, the dent remains permanently in the shock absorbing pad 3. Such impact energy absorbing structures susceptible to damage are inferior in commercial value and hence unsatisfactory.
The impact energy absorbing structure shown in FIG. 3 does not allow a dent 8 to be formed in the shock absorbing pad 3. However, the protective function and the shock resistance of the rigid cover 6 protecting the shock absorbing pad 3 spoils the energy absorbing function of the shock absorbing pad 3 and, consequently, the shock absorbing pad 3 is incapable of effectively performing the shock absorbing function.
To eliminate such disadvantages in the foregoing known impact energy absorbing structures, Japanese Utility Model Laid-open (Kokai) No. 58-118082 proposes an improved impact energy absorbing structure as shown in FIG. 4. This improved impact energy absorbing structure employs a rigid cover 6 provided with grooves 9 to reduce the rigidity of the cover to some extent. However, the grooves 9 form a rugged surface spoiling the appearance and touch of the cover 6. Furthermore, the grooves 9 require additional work for forming the cover and the operation of attaching the shock absorbing pad 3 to the cover 6 difficult, and increases costs.
The protective function of an impact energy absorbing structure as shown in FIG. 5 and having a door inner panel provided with a chest protecting pad 3a and a lumbar protecting pad 3b will be examined.
Suppose that the passenger 10 has a head 10a of a mass ml, a chest 10b of a mass m2 and a rigidity (spring constant) k.sub.2, and a lumbar region 10c of a mass m and a rigidity k.sub.3. Generally, the lumbar region 10c has a higher rigidity and resistance than chest 10b, and hence k.sub.3 &gt;k.sub.2.
Suppose that the same impact force F acts on both the chest 10b and lumbar region 10c of the passenger 10. Since the head 10a is supported on the chest 10b, the virtual mass of the chest 10b is m.sub.2 +m.sub.2. Since the head 10a and the chest 10b are supported on the lumbar region 10c, the virtual mass of the lumbar region 10c is m+.sub.1 m.sub.2 +m.sub.3. Then, according to Newton's laws of motion, EQU F=(m.sub.1 +m.sub.2).multidot..alpha..sub.2 =(m.sub.1 +m.sub.2 +m.sub.3).multidot..alpha..sub.3
where .sub.2 is the lateral acceleration of the chest 10b, and .sub.3 is the lateral acceleration of the lumbar region 10c. Under such a condition, EQU F=k.sub.2 .multidot.x.sub.2 =k.sub.3 .multidot.k.sub.3
where x.sub.2 and x.sub.3 are the respective lateral displacements of the chest 10b and the lumbar region 10c.
Thus, C.alpha..sub.2 &gt;.alpha.&gt;.sub.3 and x.sub.2 &gt;k.sub.3 when the same impact force F acts on both the chest 10b and lumbar region 10c of the passenger 10. Therefore, it is estimated that the effect of the collision of the vehicle with another vehicle is higher on the chest 10b of the passenger 10 than on the lumbar region 10c of the passenger 10.
In view of the foregoing fact, when the chest protecting pad 3a and the lumbar protecting pad 3b are the same in rigidity, the chest protecting pad 3a is excessively hard while the lumbar protecting pad 3b is excessively soft. Such an impact energy absorbing structure is unsatisfactory because the comparatively weak chest 10b of the passenger 10 is exposed to the danger of greater shocks.
The chest protecting pad 3a and the lumbar protecting pad 3b of the conventional impact energy absorbing structure are substantially the same in thickness, so that the chest protecting pad 3a and the lumbar protecting pad 3b strike substantially simultaneously against the chest 10b and the lumbar region 10c, respectively, when impact energy is imparted to the impact energy absorbing structure. As mentioned above, the rigidity of the skeletal construction and the resistance to shocks of the lumbar region are greater than those of the chest 10c.
In view of such facts, the chest 10b and lumbar region 10c of the passenger 10 will strike substantially simultaneously against the chest protecting pad 3a and the lumbar protecting pad 3b, respectively, and the chest 10b having a rigidity and resistance against shocks lower than those of the lumber region 10c may be exposed more seriously to the effect of shocks. Therefore, the impact energy absorbing structure shown in FIG. 5, as well as those shown in FIGS. 1 to 4, are not satisfactory.